The present invention relates to electric switching devices of the type employed for switching very small currents at relatively low voltages, as for example, switches employed in automotive applications in circuit arrangements operating from a 12 volt supply. In such automotive applications, it has become desirable to employ multiplexing techniques wherein the user input switches merely provide a signal to a microcomputer which generates control signals for appropriate relaying of switching power to various functional loads. Multiplexing arrangements of this type eliminate the need for much of the wiring in the vehicle needed to carry load currents to the various functions inasmuch as the connections from the user input switches to the microcomputer carry only a very small signal current, rather than load current.
In providing switches for multiplex systems, and particularly for automotive applications, it has been the practice to utilize existing user input switches to maintain the tactile characteristics and "feel" of the switching operations for user compatibility. However, the existing switches employed for typical automotive accessory applications such as window lift, actuation, and actuation of door lock solenoids have been designed to handle significant load currents and are thus overdesigned for multiplexing applications and thus add unnecessary costs in the switching arrangements.
It has therefore been desired to provide a reliable low voltage switch assembly, suitable for automotive multiplex applications which is low in manufacturing cost and capable of providing the long cycle life and environmental survivability required for automotive applications. Heretofore, it has been proposed to utilize a switch employing the sensing of changes in capacitance of a user-actuated capacitor to provide the low current low voltage switching for automotive multiplex applications. However, known techniques for providing capacitive switching have proven to be costly to manufacture and limited in capacitance per unit area and therefor prohibitive for high volume automotive passenger car usage.